Effects of dopaminergic agonists and antagonists on cerebellar guanosine-3',5'-monophosphate (cGMP)

Cerebrospinal fluid cyclic guanosine 3'5' monophosphate levels in Parkinson's disease

We measured CSF and plasma levels of cGMP in 22 patients with Parkinson's disease (PD) and in 28 age and sex-matched controls. PD patients had similar plasma cGMP levels than those of controls, although they showed a non-significant trend towards higher CSF cGMP levels (P=0.07). PD patients treated with levodopa showed significantly higher CSF cGMP levels than those not treated with this drug (P<0.01), and controls (P<0.01). However, treatment with dopamine agonists did not influence CSF cGMP levels. Plasma and CSF levels of cGMP did not correlate with age at onset, duration, and severity of PD. These results suggest that changes in the concentration of cGMP in CSF of patients with PD are not related with the disease, but rather with levodopa therapy.

Increase of cyclic GMP in cerebellum by methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM)

The intraperitoneal administration of DMCM (0.5-3 mg/kg) produced a dose-related increase in the content of cyclic GMP in the rat cerebellar cortex. The effect of DMCM on cyclic GMP was abolished by pretreatment with benzodiazepine receptor ligands, diazepam and Ro15-1788 and by the GABA agonist muscimol. The results suggest that DMCM increases cerebellar cyclic GMP content through a direct action on benzodiazepine receptors located in the cerebellar cortex. The interaction between DMCM and the GABAergic system associated with benzodiazepine receptors is discussed. Cerebellar cyclic GMP content can be used as a biochemical index to differentiate agonists and antagonists for benzodiazepine receptors.

Cerebellar pathology in schizophrenia--cause or consequence?

Atrophy of the cerebellar vermal cortex has been reported to occur in 10% or more of patients with schizophrenia. Data from studies on experimental animals indicate that a functional relationship between the cerebellum and parts of the forebrain involved in emotion exists, and that the cerebellum may influence some types of behavior. Cerebellar abnormality in schizophrenic patients, although of uncertain cause, could contribute to the symptomatology of the disease.